There will be many variations in each piece of material but generally - nylon is stronger than polyester. Polyester absorbs less water than nylon. Polyester has less 'stretch' than nylon. Polyester has a better UV resistance than nylon.

Don't view stretch as an overly bad thing as it often allows for a tighter pitch ... but will usually sag more when wet, so catch 22. The lack of stretch may also place more stress of seams, etc.

Fsir po8nt on going for the stronger material Stu... But as I'm trying to cut down weight (on a budget) and the 20d still being (hopefully) stronger than the 15d silnylon that the newer Gatewood comes in... and the fact that the lighter version hopefully (as per upur mention above above) will have a stronger UV rating...

I'll probs still go for the lighter one at £120 and see how I gets on/in

Got the new lunar solo in sil-poly. Seems good after one outing (thanks for the right sized pole Stu :). Didn't sag like sil-nylon can.

Still convinced I'm an idiot though as I did a fair bit of research and was convinced I needed the urethane(?) Sealant instead of the silicon one. It then all peeled off and I used the half finished tube of silicon I had to fix it.